Gas Valve Replacement on Water Heaters

Gas Valve Replacement on Water Heaters
May 3, 2012 Lorelie
gas valve replacement on water heaters

Gas Valve Replacement on Water Heaters Explained

The water heater gas valve or control gas valve is a small device that is situated inside the tankless water heater, or, outside in the lower part of the tank-type water heater.  It is designed to open or close the flow of gas to the pilot and the main burner.

The water heater control gas valve is designed to have a built-in safety shut-off mechanism that closes the supply to the burner and the pilot light if in case the pilot light is put out for any reason.  The electrode or thermocouple is responsible for sending the signal.

Types of Water Heater Gas Valves

There are many types of water heater gas valves.  Some of the water heater manufacturers such as Bradford White, AO Smith, and American Heater Company are utilizing Robertshaw and White-Rodgers gas control valves while some manufacturers are utilizing Honeywell gas control valves.

The Robertshaw water heater gas control valve has the following components:

  • Gas control valve with the safety valve, thermostat valve and electromagnet
  • Reset button
  • Control knob with ON-OFF pilot settings
  • Inlet and outlet
  • Water temperature dial and setting indicator
  • Thermocouple threaded port
  • Pilot tube threaded port
  • Thermal switch

The White-Rodgers water heater gas control valve has the following components:

  • Gas control valve with the safety valve, thermostat valve and electromagnet
  • Control knob with ON-OFF pilot settings
  • Inlet and outlet
  • Water temperature dial and setting indicator
  • High limit or temperature probe
  • Thermocouple threaded port
  • Pilot tube threaded port
  • Thermal switch

Review on Water Heater Gas Valve Components

There are some valves which are equipped with the manifold gas pressure tap wherein you can measure the pressure on the line supplying the main burner.  You only have to remove the plug and then attach the gas gage.  The recommended pressure is actually marked on the water heater gas valve.

Both the tube from the main burner and the pilot light tube are connected to the gas valve as well as the thermocouple which is used as the safety element.  The unit typically works on a 24 VAC, but it could also work without the presence of outside electricity.

The temperature setting indicator, which is installed on the front of the gas valve, lets you choose the right hot water temperature setting.  The temperature is usually factory set on its lowest setting in order to comply with the safety regulations.  On some control valves, namely the Robertshaw, there is a “HOT” mark that shows where the 120 F temperature or scalding water range starts.

The pilot burner is lit by means of switching the control knob to the pilot setting, or by pressing the reset button if you have a Robertshaw gas valve, and pressing the piezo igniter button.  There are some water heater units wherein you need to manually use a match in order to ignite the pilot burner.

When the pilot burner is lit, the pilot flame will then heat the thermocouple that generates a small electric current which is sufficient enough to keep the gas valve open.  Thus, when you release the knob, the gas will still continue to flow to the pilot.

Afterwards, the incoming cold water will activate the thermostat, which initiates the water heater gas valve to open to the burner.  The pilot light then ignites the gas on the main burner.  The hot water temperature rises and when it reaches the set temperature, the thermostat interrupts the main flow.

There are two metal probes which are mounted onto the back of the gas valve and immersed inside of the tank.

The longer temperature probe has a metal rod or Energy Cut Off (ECO) switch which expands and contracts as the water temperature changes.  The probe sort of acts as the temperature high limit.  If in case the water gets excessively hot, a sensor within the probe opens, and then interrupts the small electrical current to the gas valve, and thus the flow is interrupted.

Do take note that the control valve, if subjected to an excessive pressure of over 0.5 psi, can potentially damage the valve and could result in the explosion from the leaking gas.

The manual shut off valve in the gas supply line must be installed along with the sediment trap or drip leg in order to prevent foreign materials such as dirt coming into the control valve.  In order to allow for easier service, a ground joint union or flexible pipe between the shut off and water heater gas valve must be installed.

Do take note that if for any reason the water heater fails to shut down, namely due to overheating, you must always manually turn off the water heater gas control valve.

Steps on How to Remove and Replace the Water Heater Gas Valve

When you need to replace your water heater gas valve, make it a point to use factory-authorized replacement parts only.  Do take extra care when working on the gas valve.  Do not use a pipe wrench or any other similar tool to grip the body, and most of all, do not apply too much force because it might damage the element.  The removal and replacement of the water heater gas valve typically involves gas piping and electrical wiring disconnection.  Below are the steps for gas valve replacement on water heaters:

  • Turn off the manual shut-off valve on the gas line.  This is normally situated just beside the water heater.
  • On the gas control valve, turn the thermostat to its lowest setting.
  • After that, turn off the electrical power.
  • Turn the control knob to the OFF position.
  • If the situation calls for it, drain the water heater.
  • Disconnect the pilot tube, thermocouple, main tube and piezo
  • Disconnect the ground joint union as well as other connections from the gas control valve.
  • Lastly, remove the gas valve assembly.

When you are replacing the water water gas valve, ensure to match the parts and simply follow the steps above in reverse order.  Utilize approved Teflon tape or compound on all of the connections.  Do not forget to check for gas valve leaks by using soap-water solution.

Comment (1)

  1. Marvin Scott 2 years ago

    In the event the high temperature switch activates does it shut off gas to the pilot as well as the main burner

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